Maximizing the yield of highly-valued products from crude oil often results in the production of relatively heavy hydrocarbon streams which are difficult to upgrade to lighter products. Typically, these streams are the distillation bottoms resulting from the atmospheric or vacuum distillative reduction of a crude oil or a crude oil-derived feedstream. These "bottoms" fractions are known as petroleum residuum or "resid." Resids typically contain only a small amount of material boiling below about 1000.degree. F. at atmospheric pressure, up to several tens of percent of Ramsbottom carbon, and up to several hundred parts per million of metals such as nickel and vanadium.
Modern refinery economics demand that resids be aggressively processed to yield lighter and more valuable hydrocarbons. Typically, resid will be upgraded in a multi-reactor, supported catalyst system such as those disclosed in U.S. Pat. Nos. 4,940,529; 5,013,427; 5,124,025; 5,124,026, and 5,124,027, the disclosures of which are hereby incorporated by reference. While supported catalyst systems such as those disclosed in the foregoing patents have proven highly effective in upgrading heavy feedstreams such as resids, refiners continue to investigate other processes for obtaining more valuable products from resids.
Another approach for upgrading resid is to hydrotreat resid in the presence of an oil-soluble catalyst. This approach is disclosed in U.S. Pat. No. 5,055,174 and the earlier patents disclosed therein. The '174 patent teaches that hydrocarbon-containing feedstocks can be upgraded by contacting hydrogen and the hydrocarbon-containing feedstock in the presence of an oil-soluble molybdenum dithiocarbamate or a molybdenum dithiophosphate. While the process disclosed in the '174 patent may prove to be advantageous in some situations, the oil-soluble liquid catalysts disclosed therein are believed to be relatively expensive to produce and therefore may be potentially undesirable for use in a continuous refinery process.
Another approach to upgrading hydrocarbonaceous feedstocks such as resid is to introduce a soluble catalyst such as dimanganese dicarbonyl or chromium hexacarbonyl into the feedstock prior to upgrading the feedstock in the presence of hydrogen and a supported catalyst. Such an approach is disclosed in U.S. Pat. No. 4,578,180. As with the '174 patent, the processes disclosed in the '180 patent may under certain conditions prove useful, but the advantages of those processes may be limited by the cost of preparing the disclosed oil-soluble, metal-containing catalysts.
To facilitate the cost-efficient upgrading of hydrocarbon feedstocks such as resid, new catalysts and processes are required which minimize catalyst preparation costs and maximize the effectiveness of soluble catalysts under the aggressive operating conditions typically required to produce substantial quantities of lighter, more valuable products from a heavy hydrocarbon feedstock such as resid.